1. Field of the Invention
The present invention relates generally to telescoping slide assemblies. More particularly, the present invention relates to a slide assembly that occupies a reduced cross-sectional area while maintaining a high load rating.
2. Description of the Related Art
Slide assemblies are commonly used to support an object, relative to a support structure, for linear motion between an accessible and a stored position. For example, drawers are usually supported by one or more slide assemblies for movement between an open and closed position relative to a cabinet, or other enclosure. Regardless of the application, it is generally desirable for the slide assembly to occupy as small an area as possible, while still providing sufficient strength, in order to maximize the dimensions of the drawer, or other object supported by the slide asembly.
One specific application in which a reduction of the cross-sectional area of the slide assembly is especially beneficial is the internet server market. In an internet server, the hardware components comprising the server are arranged and secured within a metal or a plastic enclosure, or chassis. The server/chassis assembly is then typically housed within an enclosed cabinet containing multiple servers arranged in a vertical manner. Each chassis is mounted on a pair of telescoping slides so that the server may be easily withdrawn from the cabinet for inspection, repair or replacement. It is contemplated that 1U and 2U servers will comprise the majority of the future internet server market.
A large number of cabinets, each containing multiple internet servers, often covering thousands, or tens of thousands, of square feet of floor space may be found in a single location. Storage costs for internet servers are typically calculated on a basis of square feet of floor space occupied per server. Accordingly, it is highly desirable to reduce the area occupied by the cabinets in order to maximize the number of cabinets, and thus servers, that may be stored in a given area.
One impediment to reducing cabinet dimensions has been the cross-sectional size of the available slide mechanism, or “slide”, for short. Additionally, in an effort to reduce design and purchasing costs, it is desirable to provide a single slide that is suitable for both the 1U and 2U server applications. Therefore, a need exists for a slide of reduced cross-sectional area that is structurally capable of supporting a vertical load produced by either a 1U or 2U internet server.
In an internet server application, it is desirable to utilize an over-travel type slide assembly, which is capable of extending a distance greater than the length of any of the slide's individual segments. When utilizing an over-travel slide, the server may be completely withdrawn from the cabinet to permit access to the rearward end of the server where cables, such as power cables or connecting cables, may be located. A typical over-travel slide has three individual slide segments telescopingly engaged with one another. For example, an outer slide segment may be connected to the cabinet and an inner slide segment may be connected to the internet server chassis. An intermediate segment may interconnect the outer slide segment and the inner slide segment.
In a three piece slide assembly it is desirable for the individual slide segments to move in a specific sequence relative to one another. Specifically, it is highly undesirable for the inner segment to fully extend alone, before the intermediate slide segment begins to extend. Accordingly, the inner and intermediate slide segments are often coupled to move together, at least initially, when extending from the fully closed position of the slide. The inner and intermediate slide segments may be configured to frictionally engage one another to achieve the desired sequencing. Alternatively, a latch-type mechanism may be used to releasably connect the inner and intermediate slide segments.
However, as mentioned above, it is highly desirable to reduce the cross-sectional dimensions of the slide. To be strong enough to withstand the forces from repeated extensions of the slide assembly, latch-type mechanisms may necessarily be prohibitively large and prevent the slide assembly from having desirably small cross-sectional dimensions. Friction-type sequencing mechanisms are often unreliable in operation. For example, frictional forces between the outer and intermediate slide segments, due to the weight of the server, may be larger than the sequencing friction and allow the inner slide segment to extend alone.
An alternative method of sequencing extension of the slide segments is disclosed in U.S. Pat. No. 6,056,379 to Weng. The Weng slide assembly 1 is a three-piece, over-travel slide assembly having an inner slide segment 2, an intermediate slide segment 3 and an outer slide segment 4. An outer assembly of bearings includes both upper and lower bearings 5 positioned between the intermediate slide segment 3 and outer slide segment 4. An inner assembly of bearings includes both upper and lower bearings 6 between the intermediate slide segment 3 and inner slide segment 2.
A plurality of spherical members, or transmission members 7, are fixed for movement with the intermediate slide segment 3 as it extends and retracts. Each transmission member 7 contacts both the inner slide segment 2 and outer slide segment 4. Upper and lower sets of transmission members 7 are in contact with upper and lower end portions 8 of the inner slide segment 2 and upper and lower end portions 9 of the outer slide segment, respectively. Extension of the inner slide segment 2 results in rotation of the transmission members 7, as a result of being in contact with the end portions 8, which then roll on the end portions 9 of the outer slide segment 4. Because the intermediate slide segment 3 is fixed for movement with the transmission members 7, the rolling motion of the transmission members 7 causes extension of the intermediate segment 3 along with extension of the inner slide segment 2.
One problem with the Weng slide assembly 1 is that the provision of both outer bearings 5 and inner bearings 6 necessarily increases the height of the slide 1. As discussed above, a reduced cross-sectional envelope is highly desirable, especially in internet server mounting applications. An additional problem with the Weng slide assembly 1 is that, because both the outer and inner bearings 5, 6 and the transmission members 7 are positioned between the inner slide segment 2 and the outer slide segment 3, the tolerances of both the inner and outer segments 2, 3 must be precisely controlled in order to ensure that the transmission members 7 will properly contact both the end portions 8, 9 of the inner and outer segments 2, 4, respectively, which necessarily increases manufacturing costs. It may even be necessary to perform an additional manufacturing process step in order to ensure appropriate dimensions of the end portions 8, 9, which may increase the overall cost of the slide assembly 1 to a greater extent.